Signals are usually detected in ion cyclotron resonance-based mass spectrometry by measuring potential changes induced by the periodic motion of the ions in "antennae" electrodes. Since the induced voltage is not linear with distance for finite electrodes, the potential induced by ions moving in orbits of non-zero radius will not have a perfect sinusoidal variation with time. The signal will, therefore, contain components at higher harmonics (NF.sub.e) of the cyclotron frequency as well as at the fundamental (F.sub.e) This effect does not depend on the in homogeneity of the trapping field and is, therefore, quite general. The ion cyclotron resonance experiment is usually designed to minimize harmonic signals since they can complicate proper identification of sample ions. In the usual continuous wave (cw) experiment the harmonics are not detected because of the detecting method. Usually a phase sensitive detector is used and the detector is tuned to the fundamental frequency. In the modern Fourier transform spectrometer the harmonics are suppressed by cell design and choice of operating conditions.